Most prior techniques to treat varicose veins have attempted to heat the vessel by targeting the hemoglobin in the blood and then having the heat transfer to the vessel wall. Lasers emitting wavelengths of 500 to 1100 nm have been used for this purpose from both inside the vessel and through the skin. Attempts have been made to optimize the laser energy absorption by utilizing local absorption peaks of hemoglobin at 810, 940, 980 and 1064 nm. RF technology has been used to try to heat the vessel wall directly but this technique requires expensive and complicated catheters to deliver electrical energy in direct contact with the vessel wall. Other lasers at 810 nm and 1.06 um have been used in attempts to penetrate the skin and heat the vessel but they also have the disadvantage of substantial hemoglobin absorption which limits the efficiency of heat transfer to the vessel wall, or in the cases where the vessel is drained of blood prior to treatment of excessive transmission through the wall and damage to surrounding tissue. All of these prior techniques result in poor efficiency in heating the collagen in the wall and destroying the endothelial cells.
Baumgardner and Anderson teach the advantages of using the mid IR region of optical spectrum 1.2 to 1.8 um, to heat and shrink collagen in the dermis.
The prior art teaches manual retraction of the catheter. This is a major cause of overheating and perforation of the vessel wall as even the best surgeon may have difficulty retracting the fiber at exactly the correct speed to maintain a vessel wall heating temperature of 85 deg C. Other prior art using thermocouples at the tip of the catheter depend on electrical contact between electrodes inside the vessel and are expensive and require very slow catheter-withdrawal (2 cm/min.) and are difficult to use.
The relevant references in the prior art teach use of much higher power levels, such as between about 10 to about 20 watts. This is because the prior art laser wavelengths are not as efficiently coupled to the vessel wall and are instead absorbed in the blood or transmitted through the wall into surrounding tissue. It will be understood that methods taught in the prior art can be inefficient to such a degree that external cooling is mandatory on the skin surface to prevent burns.
Finally, the methods and apparatus taught in the prior art does not mention the use of diffusing catheter tips for varicose vein treatment. Use of common, standard, non-diffusing tip fiber optic and other laser delivery devices increases the risk for perforation of the cannulated vessel.
Navarro et al., U.S. Pat. No. 6,398,777 issued Jun. 4, 2002, teaches a device and method of treating varicose veins that involves using laser energy whose wavelength is 500 to 1100 nm and is poorly absorbed by the vessel wall. Laser energy of wavelengths from 500 to 1100 nm will penetrate 10 to 100 mm in tissue unless stopped by an absorbing chromophore. See FIG. X. Most of the energy used by this method passes through the vessel wall and causes damage to surrounding tissue. Procedures using these wavelengths can require cooling of the surface of the leg to prevent burning caused by transmitted energy. Operative complications of this technique include bruising and extensive pain caused by transmitted energy and damage to surrounding tissue.
However, this technique does appear to be clinically effective (but misleadingly so) because the blood that remains in the vein after compression absorbs the 500 to 1100 nm energy. 500 to 1100 nm light is absorbed in less than 1 mm in the presence of hemoglobin. See FIG. 10. This blood heats up and damages the vein wall by conduction, not by direct wall absorption as claimed by Navarro.
This prior art technique is poorly controlled because the amount of residual blood in the vein can vary dramatically. During an actual procedure using 500 to 1100 nm lasers it is possible to see the effects of blood absorption of the energy. At uncontrolled intervals white flashes will be seen indicating places of higher blood concentration. The blood can boil and explode in the vessel causing occasional perforation of the vein wall and unnecessary damage to healthy tissue.
In places without residual blood the laser energy has no absorbing chromophore and will be transmitted through the wall without causing the necessary damage and shrinkage claimed by the inventors.
Navaro states that the treatment device described must be in direct “intraluminal contact with a wall of said blood vessel”. This is necessary because the 500 to 1100 nm laser cannot penetrate any significant amount of blood, even though it requires a thin layer of blood to absorb and conduct heat to the vessel wall. This is very difficult to achieve and control.
Navarro also describes the delivery of energy in bursts. This is required using their technique because they have no means to uniformly control the rate of energy delivered. Navarro teaches a method of incrementally withdrawing the laser delivery fiber optic line while a laser burst is delivered. In clinical practice this is very difficult to do and results in excessive perforations and complications.
Closure of the greater saphenous vein (GSV) through an endolumenal approach with radiofrequency (RF) or lasers has been proven to be safe and effective in multiple studies. These endovenous occlusion techniques are less invasive alternatives to saphenofemoral ligation and/or stripping. They are typically performed under local anesthesia with patients returning to normal activities within 1-2 days.
RF energy can be delivered through a specially designed endovenous electrode with microprocessor control to accomplish controlled heating of the vessel wall, causing vein shrinkage or occlusion by contraction of venous wall collagen. Heating is limited to 85 degrees Celsius avoiding boiling, vaporization and carbonization of tissues. In addition, heating the endothelial wall to 85 degrees Celsius results in heating the vein media to approximately 65 degrees Celsius which has been demonstrated to contract collagen. Electrode mediated RF vessel wall ablation is a self-limiting process. As coagulation of tissue occurs, there is a marked decrease in impedance that limits heat generation.
Presently available lasers to treat varicose veins endolumenally heat the vessel by targeting the hemoglobin in the blood with heat transfer to the vessel wall. Lasers emitting wavelengths of 500 to 1064 nm have been used for this purpose from both inside the vessel and through the skin. Attempts have been made to optimize the laser energy absorption by utilizing local absorption peaks of hemoglobin at 810, 940, 980 and 1064 nm. The endovenous laser treatment (EVLT™) of the present invention allows delivery of laser energy directly into the blood vessel lumen in order to produce endothelial and vein wall damage with subsequent fibrosis. It is presumed that destruction of the GSV with laser energy is caused by thermal denaturization. The presumed target is intravascular red blood cell absorption of laser energy. However, thermal damage with resorption of the GSV has also been seen in veins emptied of blood. Therefore, direct thermal effects on the vein wall probably also occur. The extent of thermal injury to tissue is strongly dependent on the amount and duration of heat the tissue is exposed to. When veins are, devoid of blood, vessel wall rupture occurs.
One in vitro study model has predicted that thermal gas production by laser heating of blood in a 6 mm tube results in 6 mm of thermal damage. This study used a 940-nm-diode laser with multiple. 1 5Jr˜second pulses to treat the GSV. Histologic examination of one excised vein demonstrated thermal damage along the entire treated vein with evidence of perforations at the point of laser application described as “explosive-like” photo-disruption of the vein wall. Since a 940 nm laser beam can only penetrate 0.03 mm in blood (17), the formation of steam bubbles is the probable mechanism of action.
Initial reports have shown endovenous RF to have excellent short-term efficacy in the treatment of the incompetent GSV, with 96% or higher occlusion at 1-3 years with a less than 1% incidence of transient paresthesia or erythema (10-11) Although most patients experience some degree of post-operative ecchymosis and discomfort, no other major or minor complications have been reported.
Patients treated with EVLT have shown an increase in post-treatment purpura and tenderness. Most patients do not return to complete functional normality for 2-3 days as opposed to the 1 day “down-time” with RF Closure™ of the GSV. Since the anesthetic and access techniques for the two procedures are identical, it is believed that non-specific perivascular thermal damage is the probable cause for this increased tenderness. In addition, recent studies suggest that pulsed laser treatment with its increased risk for vein perforation may be responsible for the increase symptoms with EVLT vs. RF treatment. Slow uncontrolled pull-back of the catheter is likely one cause for overheating and perforation of the vessel wall as even the best surgeon may have difficulty retracting the fiber at exactly the correct speed to maintain a vessel wall heating temperature of 85 deg C. This technique prevents damage to surrounding tissue and perforation of the vessel.